Yes, it's 旧仮名使い. You see it in a lot of 国語s, e.g. 大辞林's entry: "よう やう ［1］ 【様】" where the "やう" is in a smaller font showing it's the old form (*not* pronunciation".)
It's an area where we (and most modern J-Other dictionaries don't go.

@@ -11,3 +10,0 @@
-</r_ele>
-<r_ele>
-<reb>やう</reb>

やう is merely the historical kana for the よう reading. if it needs to be recorded, i'm not sure what the best way to do so is.  it doesn't really fit [ok], as that is for archaic readings.  this is actually the same reading, just in old orthography

I often see this word pronounced "やう".

There are few examples of this on ejje.weblio.jp including "•財産権の内容は、公共の福祉に適合するやうに、法律でこれを定める。"

Another example is a movie discussed on Wikipedia entitled "妻よ薔薇のやうに". 
https://ja.wikipedia.org/wiki/妻よ薔薇のやうに

@@ -10,0 +11,3 @@
+</r_ele>
+<r_ele>
+<reb>やう</reb>

@@ -15,1 +15,1 @@
-<xref type="see" seq="2409190">様だ</xref>
+<xref type="see" seq="2409190">様だ・1</xref>
@@ -39,0 +39,1 @@
+<xref type="see" seq="2409190">様だ・2</xref>